These days grok mostly means to “get it” but also means simply to understand something thoroughly and completely. Technologists often use this watered down version of the original which first appeared in Robert Heinlein’s Stranger in a Strange Land to give a word to what Earthlings cannot explain in words other than “to understand so thoroughly that you merge with it and it merges with you.” So saying, “Yeah I grok JavaScript” would be immediately suspect to anyone who understands what the term grok actually means, but people say it anyway.